The long term objective of this proposal is to gain insight into mechanisms of host defense against infectious agents in humans, through the study of leprosy as a model. At the site of infection, organized collections of macrophages form granulomas to defend against the pathogen, Mycobacterium leprae. Our goal is to understand mechanisms of granuloma formation and function in human infectious disease. We will test the hypothesis that distinct subsets of macrophages regulate granuloma formation, and hence host defense. This will be accomplished by using bioengineered 3D microconstructs to encapsulate and confine M?, facilitating immune cell interaction, replicating the in vivo tissue microenvironment where granulomas form. Our aims are: 1) Fabricate artificial granulomas using droplet microfluidics to model human leprosy infection, and, 2) Investigate the role of macrophage subsets in granuloma formation and function. In addition we will study the function of Langhans multinucleated giant cells, a hallmark of host defense in chronic infection. Together these aims target an integrated understanding of the interaction between a microbial pathogen and host-derived M?, with the goal to uncover novel mechanisms of immune responses that contain the pathogen, which might serve as targets host-directed therapies to modulate the immune response in human infectious disease. As such, this project brings together two laboratories, the Modlin lab with expertise in cellular immunology and the Revzin lab with expertise in bioengineering microstructures to optimize cell-cell interactions, to develop a new approach to study mechanisms by which granulomas are formed and contribute to host defense in humans.